Propeller driven boats, or “air-boats” as they are commonly known, have found wide application and acceptance in areas where shallow water, reeds, everglades, partially frozen lakes and sub-surface debris present hazards to the operation of a submersed propeller. A significant advantage associated with air-boats is their ability to skim over the surface of land or water alike at high speeds, having relatively little impact on whatever lies beneath it.
An air-boat operates on the principle that once the propeller generates a rearward jet of air sufficient to overcome the friction encountered by the boat hull, the hull of the boat planes over the surface. Developing a sufficient rearward jet of air necessary to plane on land or hydroplane on water requires a significant amount of power, depending on the size and weight or the boat.
Typically, an air-boat is powered by an aircraft or automotive internal combustion engine. Aircraft engines normally include a propeller directly coupled to the crankshaft of the engine and thus are generally mounted high above the water line of the boat hull to provide adequate clearance for the rotating propeller. Automotive engines are mounted lower to the waterline and typically require a crankshaft speed reducer mounted between the engine and the propeller. The speed reducer allows the propeller to be mounted sufficiently high above the water line to provide the clearance needed for rotation.
The typical propeller used in air-boats is a two blade aircraft propeller. When the propeller is rotating at maximum speed, each of the propeller tips generate shock waves which produce a significant amount of noise. The noise generated by the propeller often limits air-boat operation to secluded areas. U.S. Pat. No. 5,839,926 teaches a system for mounting two counter-rotating propellers on a single engine for reducing the noise generated by an air-boat. While this system does provide some sound reduction, the increased complexity and cost associated with installation and maintenance deters widespread use of the system.
Air-boat propellers are usually protected by an open wire mesh cage that serves to protect boaters and fowl from the dangers associated with a rotating propeller. U.S. Pat. No. D427,562 illustrates an ornamental design for an air-boat similar to many modern constructions. While the open mesh cages provide some safety they do nothing to reduce the sound generated by the propeller.
Steering of air-boats has typically been accomplished by rudders of either the conventional submerged type or the aircraft type mounted in the slipstream of the propeller. The operation of submerged rudders may be objectionable because any submerged movable part is subject to hazards such as sub-surface debris, rocks, etc. The use of a slipstream-mounted rudder is disclosed in U.S. Pat. No. 4,015,555. The use of such rudders can be disadvantageous since they are inefficient and are characterized by sluggish response because they are dependent upon the deflection of the rearward air jet. The rearward jet of air required to turn the boat produces a substantial amount of forward thrust making navigation in cluttered areas extremely difficult or impossible with this type of construction.
An alternative method of steering an air-boat is disclosed in U.S. Pat. No. 4,005,673. This method consists of changing the direction of thrust by turning both engine and propeller together about a vertical axis. This method also has undesirable characteristics. First, turning both the propeller and engine as a unit requires substantial structural mounts to avoid instability. Second, this method has the additional disadvantage of offering no inherent self-centering characteristics. Once turned, the gyroscopic effect generated by the propeller will continue to turn the boat until such time as the operator returns the mechanism to a centered position. Third, sharp turns create the danger of moving a portion of the propeller into close proximity with passengers in the boat.
Yet another method of steering an air-boat consists of an engine coupled, via a combination of shafts and gears to a pivoting propeller support structure, as shown in U.S. Pat. No. 2,341,911. This design is disadvantageous due to its inherent complexity and because the vertical drive shaft coupling the engine and propeller may tend to induce rotation in the pivoting propeller support structure.
In general, air-boats of the prior art suffer from the same drawbacks. The primary drawback is the noise generated by the propeller. The noise substantially limits the areas where air-boats may be operated. Another drawback relating to prior art air-boats results from a general lack of controllability. A direct coupling between the engine and the propeller causes the propeller to rotate whenever the engine is running and stop when the engine stops. The direct coupling makes engine idling without forward motion difficult due to the continued air thrust being produced. The continuous thrust also limits an air-boats ability to stop or quickly slow down in emergency situations. Air-boats can be difficult to control when there is a loss of engine power which stops or reduces the slipstream of air produced by the propeller. After engine loss or failure the air-boat will generally become uncontrollable. Without the slipstream of air or a rudder extending into the water there is generally no means to turn or stop the boat. This may create extremely dangerous situations in the event that an obstruction is in the boats path.
Other known specialized air propelled vehicles include for example, U.S. Pat. No. 4,421,489 which teaches a ground effect vehicle propelled by a rearward discharge of fluid therefrom. The device includes a pair of upstanding steering vanes mounted for rotation about upstanding axes and disposed on opposite sides of the center line of the fluid path. Control structure is provided to simultaneously angularly displace the vanes about their axes of oscillation. The vanes extend rearwardly of their axes of oscillation so that opposite relative angular displacement of the vanes will cause the rear ends of the vanes to swing into close juxtaposed positions. Disadvantages of this construction include complexity of the mechanisms required to independently and accurately control the steering vanes. In addition, this construction does not provide any means for slowing down or steering the boat in the event that engine power is lost.
U.S. Pat. No. 6,725,637 teaches an air-boat for reducing aquatic plant infestation by mulching or otherwise chopping plants growing on the surface of the water as the craft moves forward along a waterway. The air-boat includes a hull with an intake port at the bow end of the craft.
While the foregoing described prior art devices have improved the art and in some instances enjoyed commercial success, there remains nonetheless a continuing need in the art for evermore improved air-boat constructions for broadening the capabilities and increasing the overall safety of air-boating.
Therefore what is needed in the art is a directional control system of the vector thrust type which may be utilized in conjunction with an air-boat which will enable the air-boat to be precisely maneuvered, braked and operated in reverse. The directional control system should be adaptable to pre-existing as well as new air-boats. The directional control system should provide increased turning and stopping abilities when compared to the prior art. The directional control system should also suppress a substantial portion of the sound generated by a rotating propeller to allow air-boat use in residential or cluttered areas.